CAREER: Predicting granular flows: Amorphous continuum modeling with a length-scale

1253228PI：Kamrin密颗粒流缺乏可预测的通用模型是工程应用的障碍，也是工业中一个昂贵的问题。对于发育良好的流动，已经提出了某些流变学方法，但这些方法在运动较慢的区域被分解，在那里观察到了明显不同的行为，多年来一直拒绝理论处理。建立一个结合了快、慢两种状态的颗粒流通用模型，并为瞬变效应建立适当的塑性关系，将是该领域的一大进步，也是工程设计和地球物理中的一个有利可图的工具。受最近乳状液流动研究的成功启发，该项目将研究一种非局部本构方法，其直接包含颗粒长度尺度可能会弥补缺失的部分。通过复杂和定制的有限元工具，初步测试表明，这种策略可以在多种流动几何结构中实现定量准确的流动预测，其中包括一类以前从未用连续介质模型描述过的几何图形。将进行某些额外的测试，以澄清该模型的潜在限制。为了超越良好发展的行为并拓宽模型，将进行研究，将该技术合并到临界状态框架内，以捕捉瞬时膨胀/强化/软化效应。另一个目的是建立一个改进的非局域机制理论，从而改进对边界条件和薄体效应的解释。一旦以这种方式理解了干流，就应该再次利用增强的有限元工具来模拟流体饱和的颗粒。这一模型的相似基础和用于乳剂的相关方法在颗粒物质和其他无定形物质之间得出了重要的联系。流动诱导流动的机制及其复制流动和应力场的能力如此准确地表明了一幅微观图景，可以解决颗粒流动问题中的许多悬而未决的问题。理论研究将有助于阐明这一基本机制，以提高对其他问题的概括性。为实现非局部颗粒流模型而开发的有限元工具也为模拟颗粒系统中的多重耦合效应-如上所述的流体渗透性--打开了大门，但可以想象的是，其他效应的组合，如电场相互作用、扩散物种效应和热传导。由于颗粒流在工业、科学和工程中的许多基本应用，我们提出的方法及其被证明的准确性将为一般情况下的流动预测提供关键工具。将要开展的工作还涉及一个重要和综合的教育部分。PI在麻省理工学院的在线教育方面进行了几次创新，并提出了一些使用在线工具改善住宿和公共教育的方法。演讲还将在麻省理工学院少数民族科学与工程导论项目中进行，这是一个为期六周的暑期项目，鼓励有才华的少数民族学生攻读技术领域的学位。此外，PI将让本科生参与研究过程，并将研究问题融入到他的教学中。将通过继续组织新英格兰材料和结构力学研讨会以及APS离散材料连续描述小型研讨会，在科学界产生更广泛的影响。

1253228PI: KamrinThe lack of a predictive, general model for dense granular flow is an obstacle in engineering applications and an expensive problem in industry. For well-developed flows, certain rheological approaches have been put forward, however these break down in regions of less rapid motion, where a markedly different behavior is observed that has resisted theoretical treatment for years. To produce a general granular flow model that combines the fast and slow regimes, together with appropriate plasticity relations for transient effects, would constitute a major step forward in the field and a lucrative tool in engineering design and geophysics. Inspired by recent successes in the study of emulsion flow, this project will investigate a nonlocal constitutive approach, whose direct inclusion of a particle length-scale may provide the missing piece. With sophisticated and customized finite-element tools, preliminary tests indicate that this strategy leads to quantitatively accurate well-developed flow predictions in multiple flow geometries, including one family of geometries whose flow fields have never previously been described by a continuum model. Certain additional tests will be performed to clarify potential limitations of the model. To move beyond well-developed behavior and broaden the model, research will be conducted to merge the technique within a critical-state framework to capture transient dilation/strengthening/softening effects. Another aim is to build an improved theory for the nonlocal mechanism, and in so doing improve the interpretation of boundary conditions and thin-body effects. Once dry flows are understood in this way, enhanced finite-element tools shall be taken advantage of yet again to model fluid-saturated grains. The similar foundations of this model and related approaches used for emulsions draw important connections between granular matter and other amorphous materials. The flow-induces-flow mechanism and its ability to reproduce flow and stress fields so accurately suggests a microscopic picture that could solve many open questions in particulate flow problems. The theoretical investigation will help clarify this basic mechanism to improve generalization to other matter. The finite-element tools developed to implement the nonlocal granular flow model also open the door to modeling multiple coupled effects in particulate systems --- fluid permeability as mentioned, but conceivably a combination of other effects like electric-field interactions, diffusing species effects, and heat conduction.Owing to the many fundamental applications of granular flow in industry, science, and engineering, the approach we propose together with its demonstrated accuracy will provide a key tool for predicting flows in general circumstances. The work to be carried out also involves a significant and integrated educational component. The PI has conducted several innovations in online education at MIT and proposes a number of ways to improve residential and public education using online tools. Presentations will also be made in the MIT Minority Introduction to Science and Engineering program, a six-week summer program encouraging talented minority students to pursue degrees in technical fields. Moreover, the PI will involve undergraduates in the research process and integrate research problems into his teaching. Broader impact within the scientific community will be made through continued organization of the New England Workshop on the Mechanics of Materials and Structures, and the APS mini-symposium Continuum Descriptions of Discrete Materials.